Frame Rate Conversion Method and Image Processing Apparatus Thereof

ABSTRACT

A frame rate conversion method includes detecting a plurality of input frames to determine an image mode corresponding to the plurality of input frames; performing motion estimation on the plurality of input frames to generate a motion estimation result; and interpolating a plurality of interpolated frames according to the determined image mode, the motion estimation result and the plurality of input frames to generate a plurality of converted output frames, wherein a frame rate of the outputted frames is different from that of the input frames.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application is based on Taiwan, R.O.C. patent applicationNo. 100128602 filed on Aug. 10, 2011.

FIELD OF THE INVENTION

The present invention relates to an image processing mechanism, and moreparticularly, to a frame rate conversion method and an image processingapparatus thereof.

BACKGROUND OF THE INVENTION

Due to maturity and development of digital display technologies, acurrent display can support high-rate frame display, e.g., the currentdisplay can display an image with 100 or 200 frames every second.However, processing in a film mode, since a film is formed by recording24/25 frames per second, is different from processing a mere video thatis formed by recording and transmitting 50/60 (or 100/200) frames persecond. A frame generation rate in film mode does not match with a framedisplay rate of a display, and changes according to different filmmodes. If frames filmed in the film mode are converted using aninappropriate frame conversion rate mechanism for frames to be displayedon the display, human eyes may easily recognize defects in the display.Therefore, a flexible image processing mechanism for converting framerates of various types of film modes to accurately and efficientlyconform to a display is extremely important.

SUMMARY OF THE INVENTION

Therefore, one object of the present invention is to provide an imageprocessing apparatus for frame rate conversion and associated methods ofoperation thereof that are capable of determining a film mode of inputframes, and determining a corresponding frame interpolation techniqueaccording to the determined film mode, so as to accurately process theframes filmed in different film modes to conform to a particular formatfor display.

According to an embodiment of the present invention, a frame rateconversion method comprises detecting a plurality of input frames todetermine an image mode corresponding to the plurality of input frames;performing motion estimation on the plurality of input frames togenerate a motion estimation result; interpolating a plurality ofinterpolated frames according to the determined image mode, the motionestimation result and the plurality of input frames to generate aplurality of converted output frames, wherein a frame rate of the outputframes is different from that of the input frames.

According to another embodiment of the present invention, an imageprocessing apparatus applied for frame rate conversion comprises a modedetermining circuit and an image generating circuit. The modedetermining circuit detects a plurality of input frames and determinesan image mode corresponding to the plurality of input frames. The imagegenerating circuit coupled to the mode determining circuit performsmotion estimation on the plurality of input frames to generate a motionestimation result, and interpolates a plurality of interpolated framesaccording to the determined image mode, the motion estimation result andthe plurality of input frames to generate a plurality of convertedoutput frames. A frame rate of the output frames is different from thatof the input frames.

The advantages and spirit related to the present invention can befurther understood via the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image processing apparatus inaccordance an embodiment of the present invention.

FIG. 2 is a schematic diagram of generation of output frames F_OUTaccording to input frames F_IN via the image processing apparatusillustrated in FIG. 1.

FIG. 3 is a flow chart of operations of the image processing apparatusillustrated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of an image processing apparatus 100 inaccordance with an embodiment of the present invention. The imageprocessing apparatus 100 generates a plurality of output frames F_OUTaccording to a plurality of input frames F_IN. A frame rate of theoutput frames F_OUT is designed to be higher than the rate of the inputframes; however, it shall not be construed as limiting the presentinvention. In another embodiment, the frame rate of the output framesF_OUT is designed to be lower than the rate of the input frames F_IN. Itis noted that the frame rate of the output frames F_OUT is typicallydifferent from that of the input frames F_IN. In other words, the imageprocessing apparatus 100 performs frame rate conversion. The imageprocessing apparatus 100 converts frames in a film mode (correspondingto a frame generation rate of filming a film) to frames to be displayedon a display (corresponding to a frame display rate of the display);however, it shall not be construed as limiting the present invention.Referring to FIG. 1, the image processing apparatus 100 comprises a modedetermining circuit 105, a storage circuit 110, and an image generatingcircuit 115. The mode determining circuit 105 detects image data of theplurality of input frames F_IN to determine an image mode correspondingto the plurality of input frames F_IN. The storage circuit 110temporarily stores the image data of the input frames F_IN and providespixel data of the frames to the mode determining circuit 105. Inaddition, the storage circuit 110 provides the frame data to the imagegenerating circuit 115. The image generating circuit 115 performs motionestimation on the input frames F_IN to generate a motion estimationresult MV, and interpolates a plurality of interpolated frames accordingto the image mode determined by the mode determining circuit 105, thegenerated motion estimation result MV and the input frames F_IN togenerate a plurality of converted output frames F_OUT. In other words,in this embodiment, the current corresponding image mode is determinedaccording to the input frames F_IN, and the foregoing output framesF_OUT are generated according to the corresponding image mode, which isone of a plurality of different film modes, e.g., 3:2 pull down filmmode and 2:2 pull down film mode. Different film modes correspond todifferent frame generation rates. Since a frame display rate of adisplay is usually fixed, it is inappropriate to convert all framesfilmed at one single filming rate into frames to be displayed.Therefore, the image processing apparatus 100 is capable of determininga film mode (switching between two different film modes), and selectinga corresponding frame generation mechanism according to the determinedfilm mode to meet requirements of current users and devices.

For example, the mode determining circuit 105 comprises a mode detector1051 and a control unit 1052. The mode detector 1051 detects theplurality of input frames F_IN to generate a plurality of frame indexescorresponding to the plurality of input frames F_IN. The control unit1052 coupled to the mode detector 1051 determines an image modecorresponding to the plurality of input frames according to theplurality of frame indexes, which are for marking whether acorresponding group of consecutive frames are repeated frames. When themode detector 1051 detects that one group of consecutive frames arerepeated frames, the frame indexes corresponding to the frame indexesare defined as the same, i.e., the frame indexes corresponding tonon-repeated frames are different. For example, the input frames F_INfilmed in the 3:2 pull down film mode comprise a group of threeconsecutive repeated frames followed by a group of two consecutiverepeated frames (but the two groups of frames are not repeated frames),so that the mode detector 1052 generates a group of three consecutiverepeated frame indexes followed by a group of two consecutive repeatedframe indexes according to the foregoing image characteristics, and sucharrangement information of the frame indexes can indicate that thecorresponding input frames are filmed in the 3:2 pull down film mode. Inaddition, the input frames F_IN filmed in the 2:2 pull down film modecomprise a group of two consecutive repeated frames followed by a groupof two consecutive repeated frames (but the two groups of frames are notrepeated frames), so that the mode detector 1051 generates one group oftwo consecutive repeated frames indexed followed by another group of twoconsecutive repeated frames, and such arrangement information of theframe indexes can indicate that the corresponding input frames arefilmed in the 2:2 pull down film mode. When the input frames F_INcomprise a video A filmed in the 3:2 pull down film mode and anothervideo B filmed in the 2:2 pull down film mode, the video A has a groupof three consecutive repeated frames and a next group of two consecutiverepeated frames, and the video B has a group of a group of twoconsecutive repeated frames and a next group of two consecutive repeatedframes. Therefore, when the mode detector 1051 generates and defines theframes indexes, the frames indexes corresponding to the video A aredefined as a group of three consecutive repeated frame indexes and anext group of two consecutive repeated frame indexes, and the framesindexes corresponding to the video B are defined as being a group of twoconsecutive repeated frame indexes and a next group of two consecutiverepeated frame indexes. Accordingly, when the image processing apparatus100 receives and processes the video A of the input frames F_IN, thecontrol unit 1052 determines that the current frame is in the 3:2 pulldown film mode according to the arrangement manner and the number of theframe indexes defined by the mode detector 1051. After that, when theimage processing apparatus 100 receives and processes the video B of theinput frames F_IN, the control unit 1052 determines that the currentframe is in the 2:2 pull down film mode according to the arrangementmanner and the number of the frame indexes defined by the mode detector1051. In other words, the control unit 1052 switches the film modecorresponding to the current frame from a first film mode (i.e., the 3:2pull down film mode) to a second film mode (i.e., the 2:2 pull down filmmode). When a time sequence of the foregoing video B is earlier thanthat of the video A, in the event that the film mode is switched, thecontrol unit 1052 switches the film mode corresponding to the currentframe from the second film mode (i.e., the 2:2 pull down film mode) tothe first film mode (i.e., the 3:2 pull down film mode).

It is to be noted that in this example, the first film mode is an M:Npull down film mode, but the invention is not limited to the 3:2 pulldown film mode, and the second film mode is an L:N pull down film mode,but the invention is not limited to the 2:2 pull down film mode, whereL, M and N are positive integers, and L is different from M. Inaddition, since the corresponding film mode is determined by the controlunit 1052 with reference to the frame indexes generated by the modedetector 1051, the frame indexes are regarded as image mode informationof corresponding frames, and the approach of adopting the frame indexesto represent the detected image mode information is only for the purposeof explanation, and shall not be construed as limiting the presentinvention. In addition, when the mode detector 1051 detects whether agroup of consecutive frames are repeated frames by performing pixel datamatching, i.e., it is detected whether each of the group of frames areidentical to each other. It is to be noted that, in this embodiment,when determining whether two frames are repeated frames, the two framesare determined to be repeated frames while a pixel difference betweenthe two frames is not beyond a predetermined range (i.e., some pixelcalculation errors are allowed in this embodiment), and once the pixeldifference is beyond the predetermined range, the two frames then aredetermined as not repeated frames. In other words, when two frames arenot completely identical to each other but they have the same imagecharacteristics (i.e., the pixel difference between them is smaller thanthe predetermined range), the mode detector 1051 determines that the twoframes are repeated frames.

When the control unit 1052 determines the film mode corresponding to thecurrent frame, the determination result of the film mode is outputted tothe image generating circuit 115, which performs frame interpolationaccording to the determined film mode to generate the output framesF_OUT. For example, the image generating circuit 115 comprises a motionestimator 1151 and an image generating unit 1152. The motion estimator1151 performs image motion estimation on the input frames F_IN togenerate a corresponding motion estimation result (i.e., a motionvector). The image generating unit 1152 coupled to the motion estimator1151 generates to-be-interpolated frames according to the generatedmotion estimation result to generate the output frames F_OUT. Refer toFIG. 2 showing a schematic diagram of generation of output frames F_OUTaccording to input frames F_IN via the image processing apparatusillustrated in FIG. 1. The input frames F_IN comprises the video Afilmed in the 3:2 pull down film mode and the video B filmed in the 2:2pull down film mode. The video A comprises a group of three repeatedframes (frames 0 to 2) and a next group of two repeated frames (frames 3to 4), and the video B comprises a group of two repeated frames (frames5 to 6) and a next group of two repeated frames (frames 7 to 8).Therefore, when the mode detector 1051 defines corresponding frameindexes, with respect to the video A, the frame indexes comprise a groupof three identical frame indexes (marked by a triangle “Δ”) and a nextgroup of two identical frame indexes (marked by a box “□”), and withrespect to the video B, the defined frame indexes comprise a group oftwo identical frame indexes (marked by a circle “◯”) and a next group oftwo identical frame indexes (marked by an X “□”). Referring to FIG. 2,contents of the frame indexes are represented by INDEX, and frameshaving the same contents INDEX are repeated frames. Therefore, when theframe indexes are sequentially inputted into the control unit 1052, thecontrol unit 1052 analyzes and determines that the video A is filmed inthe 3:2 pull down film mode and the video B is filmed in the 2:2 pulldown film mode according to the contents of the frame indexes.

In practical applications, the output frames F_OUT are generated at timepoints marked by a plurality of rectangles as illustrated in FIG. 2,i.e., a frame rate of the output frames F_OUT is twice that of the inputframes F_IN, and the number of the output frames F_OUT is twice that ofthe input frames F_IN. For example, the video A of the input frames F_INcomprises five frames F0 to F4, and a corresponding video of the outputframes F_OUT comprises ten converted output frames f0 to f9. Inaddition, in this embodiment, the frames that are referred to by themotion estimator 1151 for generating the motion estimation result and aprevious frame and a next frame that are referred to by the imagegenerating unit 1152 for performing frame interpolation are respectivelyrepresented by F_P and F_N. For example, when a current film mode is thefirst film mode (i.e., the image processing apparatus 100 receives andprocesses the video A), with respect to the first to fifth output framesf0 to f4, the motion estimator 1151 calculates a motion estimationresult (i.e., an initial motion vector) with reference to the frames F0and F3 (i.e., the first frame of each of the two groups of repeatedinput frames), and the image generating unit 1152 performs frameinterpolation with reference to a previous input frame and a next inputframe, i.e., the frames F0 and F3. Accordingly, when the motionestimator 1151 estimates and outputs the motion estimation result to theimage generating unit 1152, the image generating unit 1152 calculatescorresponding motion vectors for generating the first to fifth outputframes f0 to f4 according to the motion estimation result (e.g., theinitial motion vector). Referring to FIG. 2, items MI and RATErespectively represent whether to perform frame interpolation at thegiven time points to generate the output frames and motion vector ratesapplied for performing the frame interpolation. When the item MI is “0”at one time point, it indicates that image mixing is performed on theprevious input frame F_P and the next input frame F_N instead of frameinterpolation to generate the output frame at this time point; when theitem MI is “1” at one time point, it indicates that frame interpolationis performed to generate the output frames at this time point. Themotion vector rates indicated by the item RATE are proportional to theinitial motion vector outputted by the motion estimator 1151. Forexample, the second to the fifth frames f1 to f4 correspond to the samemotion estimation result (i.e., the same initial motion vector)generated by the motion estimation 1051. In order to distinguish byhuman eyes contents displayed by the second to fifth output frames f1 tof4, the image generating unit 1152 defines the motion vector ratesindicated by the item RATE as different values, e.g., the imagegenerating unit 1152 defines the item RATE corresponding to the secondto the fifth output frames f1 to f4 as 1/5, 2/5, 3/5 and 4/5,respectively. After that, frames are interpolated according to thecorresponding item RATE, the initial motion vector of the motionestimation result and the previous and next frames F_P and F_N to serveas the output frames f1 to f4. Otherwise, the image generating unit 1152performs image mixing on the previous input frame F0 and the next frameF3 to generate the output frame f0. It is to be noted that, since themotion vector rates, at the time points, indicated by the item RATE areproportionally added, human eyes can perceive an image that is smoothlymoved when observing the interpolated frames without being aware of anyabnormal phenomena such as sudden stops or sudden accelerations.

When the current film mode is the first film mode, with respect to thesixth to the tenth output frames f5 to f9, the motion estimator 1151calculates the motion estimation result (i.e., the initial motionvector) with reference to the input frames F3 and F5 (i.e., the firstframe of each of the groups of repeated frames). The image generatingunit 1152 performs frame interpolation with reference to a previousframe and a next frame, which are respectively the frames F3 and F5.Therefore, when the motion estimation result is estimated and outputtedto the image generating unit 1152, the image generating unit 1152calculates motion vectors for generating the sixth to tenth outputframes f5 to f9. When the sixth output frame f5 is generated, the itemMI “0” indicates that frame interpolation is not performed to output thesixth output frame f5; when the seventh to tenth output frames f6 to f9are generated, the item MI “1” indicates that frame interpolation isperformed to output the seventh to tenth output frames f6 to f9.Therefore, the image generating unit 1152 performs image mixing on theprevious input frame F2 and the next input frame F5 to generate theoutput frame f5. Since the seventh to tenth output frames correspond tothe same motion estimation result (i.e., the same initial motion vector)generated by the motion estimator 1051, in order to distinguish by humaneyes contents displayed by the seventh to tenth output frames f6 to f9,the image generating unit 1152 defines corresponding motion vector ratesindicated by the item RATE as different values, e.g., the imagegenerating unit 1152 defines the item RATE corresponding to the seventhto the tenth output frames f6 to f9 as 1/5, 2/5, 3/5 and 4/5,respectively. After that, interpolated frames are generated according tothe corresponding item RATE, the initial motion vector of the motionestimation result and the previous and next input frames F3 and F5 toserve to the output frames f6 to f9. Since the motion vector rates, atthe time points, indicated by the item RATE are proportionally added,human eyes can perceive an image that is smoothly moved when observingthe interpolated frames without being aware of any abnormal phenomenasuch as sudden stops or sudden accelerations.

When the current film mode is the second film mode, with respect to theeleventh to fourteenth output frames f10 to f13, the motion estimator1151 calculates the motion estimation result (i.e., the initial motionvector) with reference to the input frames F5 and F7 (i.e., the firstframe of each group of repeated frames). The image generating unit 1152performs frame interpolation with reference a previous and a nextframes, which are the frames F5 and F7, respectively. Therefore, whenthe motion estimator 1151 estimates and outputs the motion estimationresult to the image generating unit 1152, the image generating unit 1152calculates and generates motion vectors corresponding to the eleventh tofourteenth output frames f10 to f13 according to the motion estimationresult. When the eleventh output frame f10 is outputted, the item MI “0”indicates that frame interpolation is not performed to generate theeleventh output frame f10. When the twelfth to fourteenth output framesf11 to f13 are generated, the item “1” indicates that frameinterpolation is performed to generate the twelfth to fourteenth outputframes f11 to f13. Therefore, the image generating unit 1152 performsimage mixing on the previous input frame F5 and the next input frame F7to generate the output frame f10. Since the twelfth to fourteenth outputframes f11 to f13 correspond to the same motion estimation result (i.e.,the same initial motion vector), in order to distinguish by human eyescontents displayed by the twelfth to fourteenth output frames f11 tof13, the image generating unit 1152 defines the motion vector ratesindicated by the item RATE as different values, e.g., the imagegenerating unit 1152 defines the item RATE corresponding to the twelfthto fourteenth output frames f11 to f13 as 1/4, 2/4 and 3/4,respectively. After that, the image generating unit 1152 generates theinterpolated frames according to the corresponding item RATE, theinitial motion vector of the motion estimation result and the previousand next input frames F5 and F7 to serve as the output frames f11 tof13.

When the current film mode is the second film mode, with respect to thefifteenth to eighteenth output frames f14 to f17, the motion estimator1151 calculates the motion estimation result (i.e., the initial motionvector) with reference to the input frames F7 and F9 (i.e., the firstframe of each group of repeated frames). The image generating unit 1152performs frame interpolation with reference a previous and a nextframes, which are the frames F7 and F9, respectively. Therefore, whenthe motion estimator 1151 estimates and outputs the motion estimationresult to the image generating unit 1152, the image generating unit 1152calculates and generates motion vectors corresponding to the fifteenthto eighteenth output frames f14 to f17 according to the motionestimation result. When the fifteenth output frame f14 is outputted, theitem MI “0” indicates that frame interpolation is not performed togenerate the fifteenth output frame f14. When the sixteenth toeighteenth output frames f15 to f17 are generated, the item “1”indicates that frame interpolation is performed to generate thesixteenth to eighteenth output frames f15 to f17. Therefore, the imagegenerating unit 1152 performs image mixing on the previous input frameF7 and the next input frame F9 to generate the output frame f14. Sincethe sixteenth to eighteenth output frames f15 to f17 correspond to thesame motion estimation result (i.e., the same initial motion vector), inorder to distinguish by human eyes contents displayed by the sixteenthto eighteenth output frames f15 to f17, the image generating unit 1152defines the motion vector rates indicated by the item RATE as differentvalues, e.g., the image generating unit 1152 defines the item RATEcorresponding to the sixteenth to eighteenth output frames f15 to f17 as1/4, 2/4 and 3/4, respectively. After that, the image generating unit1152 generates the interpolated frames according to the correspondingitem RATE, the initial motion vector of the motion estimation result andthe previous and next input frames F7 and F9 to serve as the outputframes f15 to f17.

It is to be noted that, in this embodiment, the video A filmed in the3:2 pull down film mode and the video B filmed in the 2:2 pull down filmmode are described for illustrating the frame interpolation flow;however, it shall not be construed as limiting the present invention.That is, videos filmed in other pull down film modes or videoscomprising a plurality of frames can also be processed according to theflow. In addition, in another embodiment, the image generating unit 1152also adopts other mechanisms to define the rates of the item RATE, i.e.,the foregoing motion vector rates (being proportionally added) indicatedby the item RATE is only described for illustration purposes, and itshall not be construed as limiting the present invention. In addition,the spirit of the foregoing frame interpolation method is describedbelow. Since different numbers of frames exist during a time interval inan original mode (i.e., when the input frames is in the 3:2 pull downfilm mode, three frames and other two frames respectively exist during atime interval), i.e., moving speeds of a motion object in the frames aredifferent according to the input frame rate (e.g., in the 3:2 pull downfilm mode, when the moving objects moves a distance covering 30 pixelpoints, the moving speed of the motion object of each of the threeframes is 5 pixel points per frame, and the moving speed of the motionobject of each of the other two frames is 7.5 pixel points per frame),human eyes may perceive abnormal phenomena of sudden stops and suddenacceleration when observing the interpolated images for the reason thatthe moving speeds of the motion objects of the frames are different.When a certain multiple of output frames are generated, more frames areoutputted during a time interval, so that an interval corresponding toeach output frame becomes shorter and thus the abnormal phenomena becomemore apparent. In order to solve this problem, the motion vector isaveraged according to different frame statuses (e.g., when five framesare interpolated to three frames, the motion vector is divided with 5,so that each frame is assigned the same moving distance, i.e., the samemoving speed/rate) to equalize each motion vector. Results obtained byrespectively multiplying the motion vector rates by the previous frameand the next frame are summed up to generate a predetermined outputframe (e.g., results of multiplying 4/5 by the input frame F0 andmultiplying 1/5 by the input frame F3 are summed up to generate theoutput frame f1, and results of multiplying 3/5 by the input frame F0and multiplying 2/5 by the input frame F3 are summed up to generate theoutput frame f2, wherein a summation of the multiplied motion vectorrates of the input frames F0 and F3 is 1).

In order to better understand the spirit of the present invention, referto FIG. 3 showing an operation flow of the image processing apparatus100 as illustrated in FIG. 1. In Step 305, the image processingapparatus 100 detects a plurality of input frames F_IN to generate frameindexes respectively corresponding to the plurality of input framesF_IN. In Step 310, the image processing apparatus 100 determines orswitches film modes corresponding to different images of the inputframes F_IN according to the frame indexes. In Step 315, the imageprocessing apparatus 100 performs motion estimation on the input framesF_IN to generate a motion estimation result MV. In Step 320, the imageprocessing apparatus 100 generates a plurality of motion vectorsaccording to the determined film mode and the motion estimation resultMV. In Step 325, the image processing apparatus 100 performscorresponding frame interpolation according to the determined pluralityof motion vectors to generate output frames F_OUT.

In addition, in other embodiments, when the motion estimation result ofthe motion estimator 1151 indicates a static video, the image generatingunit 1152 generates different interpolated frames with reference todifferent input frames to effectively increase discrimination of imagesthat observed by human eyes. For example, the image generating unit 1152generates a first interpolated frame with reference to a first frame, ofthe input frames F_IN, corresponding to an image mode, and generates asecond interpolated frame with reference to a second frame, of the inputframes F_IN, corresponding to the same image mode. The first frame andthe second frame correspond to the same frame indexes. Referring to FIG.2, taking the video A as an example, the input frames F0 and F1correspond to the same frame index. In the foregoing embodiment, theimage generating unit 1152 performs frame interpolation with referenceto the input frames F0 and F3 (respectively regarded as the previous andnext input images) to generate different output frames f1 to f4. Oncethe video A is determined as a static video, the image generating unit1152 performs frame interpolation with reference to the previous image,i.e., the input frame F1, instead of the input frame F0. In addition,the image generating unit 1152 performs frame interpolation withreference to the next image, i.e., the input frame F3 or F4, instead ofthe input frame F2. For example, when the output frame f1 is to beoutputted, the image generating unit 1152 performs frame interpolationwith reference to the input frames F0 and F3 to generate the outputframe f1; when the output frame f2 is to be outputted, the imagegenerating unit 1152 performs frame interpolation with reference to theinput frames F1 and F2 to generate the output frame f2, or the imagegenerating unit 1152 performs frame interpolation with reference to theinput frames F1 and F3 to generate the output frame f2. As for thestatic video, a majority of the image is not moved, i.e., image contentsof two adjacent frames have subtle differences. Therefore, differentinput frames are adopted to perform frame interpolation so as togenerate different adjacent output frames, and accordingly, human eyescan perceive enough image information when observing aframe-rate-converted image. It is to be noted that, in this embodiment,the operation of adopting different input frames to generate differentoutput frames is applied when a certain video is a static video, forexample. That is to say, when the video is determined as a dynamicvideo, different output frame are also generated with reference todifferent input frames according to the present invention. For example,when the video A is determined as the dynamic video, the imagegenerating unit 1152 performs frame interpolation with reference to theinput frames F1 and F2 to generate the output frame f2.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not to be limited to the aboveembodiments. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A frame rate conversion method, comprising: detecting an image modefor a plurality of input frames; performing motion estimation on theplurality of input frames to generate a motion estimation result; andinterpolating a plurality of interpolated frames according to thedetected image mode, the motion estimation result and the plurality ofinput frames to generate a plurality of converted output frames, whereina frame rate of the output frames is different from that of the inputframes.
 2. The method as claimed in claim 1, wherein the step ofdetermining the image mode corresponding to the plurality of inputframes comprises: detecting the plurality of input frames to generate aplurality of frame indexes respectively corresponding to the pluralityof input frames; and determining the corresponding image mode of theplurality of input frames according to the plurality of frame indexes.3. The method as claimed in claim 2, wherein the step of determining thecorresponding image mode of the plurality of input frames comprises:determining corresponding image modes of the plurality of input framesaccording to image characteristics indicated by the plurality of frameindexes.
 4. The method as claimed in claim 2, wherein the step ofdetecting the plurality of input frames to generate the plurality offrame indexes respectively corresponding to the plurality of inputframes comprises: receiving the plurality of input frames; determiningwhether the plurality input frames comprise consecutive frames with sameimage characteristics, and when there are consecutive repeated frames inthe input frames, determining that the consecutive repeated frames havethe same image characteristics; and defining a plurality of frameindexes corresponding to the consecutive frames as identical indexes. 5.The method as claimed in claim 2, the image mode comprising a first filmmode and a second film mode, the method further comprising: determininga current image mode as the first film mode when a current first groupof consecutive frame indexes of the plurality of frame indexes indicatesfirst image characteristics; and determining that the current image modeis switched from the first film mode to the second film mode when acurrent second group of consecutive frame indexes of the plurality offrame indexes indicates second image characteristics
 6. The method asclaimed in claim 1, wherein the step of adaptively determining the imagemode corresponding to the plurality of input frames comprises:determining an image mode corresponding to a first group of frames ofthe plurality of input frames as a first film mode; and determining animage mode corresponding to a second group of frames of the plurality ofinput frames as a second film mode, with the first film mode being anM:N film mode, the second film mode being an L:N film mode.
 7. Themethod as claimed in claim 1, wherein the step of determining the imagemode corresponding to the plurality of input frames comprises:determining an image mode corresponding to a group of consecutive framesof the plurality of input frames with the same image characteristics asa first film mode or a second film mode according to the number ofconsecutive frames.
 8. The method as claimed in claim 7, wherein thestep of interpolating the plurality of interpolated frames comprises:when the image mode is the first film mode, calculating a plurality ofmotion vectors according to the motion estimation result and a firstgroup of frame indexes, of the plurality of frame indexes, correspondingto the first film mode, with the motion vectors being assigned equalmoving distances; multiplying the frames corresponding to the firstframe indexes by a first rate and multiplying frames corresponding to asecond group of frame indexes by a second rate according to thecalculated motion vectors and the second group of frame indexescorresponding to the first film mode to respectively generate aplurality of interpolated frames, with a summation of the first rate andthe second rate being 1; and outputting the plurality of convertedoutput frames according to the plurality of input frames and theplurality of interpolated frames.
 9. The method as claimed in claim 8,wherein the step of interpolating the plurality of interpolated framescomprises: when the image mode is the second film mode, calculating theplurality of motion vectors according to the motion estimation resultand a second group of frame indexes, of the plurality of frame indexes,corresponding to the second film mode.
 10. The method as claimed inclaim 1, wherein the step of interpolating the plurality of interpolatedframes to generate the plurality of converted output frames comprises:when the motion estimation result indicates a static video: generating afirst interpolated frame with reference to a first frame, of theplurality of input frames, corresponding to the image mode; andgenerating a second interpolated frame with reference to a second frame,of the plurality of input frames, corresponding to the image mode;wherein the first frame and the second frame correspond to the sameframe indexes.
 11. An image processing apparatus configured to performframe rate conversion, comprising: a mode detecting circuit, fordetecting an image mode for a plurality of input frames; and
 12. Animage generating circuit, coupled to the mode determining circuit, forperforming motion estimation on the plurality of input frames togenerate a motion estimation result, and interpolating a plurality ofinterpolated frames according to the detected image mode, the motionestimation result and the plurality of input frames to generate aplurality of converted output frames, with a frame rate of the outputframes being different from that of the input frames. The imageprocessing apparatus as claimed in 11, wherein the mode determiningcircuit comprises: a mode detector, for detecting the plurality of inputframes to generate a plurality of frame indexes respectivelycorresponding to the plurality of input frames; and a control unit,coupled to the mode detector, for adaptively determining the image modecorresponding to the plurality of input frames according to theplurality of frame indexes.
 13. The image processing apparatus asclaimed in claim 12, wherein the control unit adaptively determinesimage modes respectively corresponding to the plurality of input framesaccording to image characteristics respectively indicated by theplurality of frame indexes.
 14. The image processing apparatus asclaimed in claim 12, wherein the mode detector receives a plurality ofinput frames, determines whether the plurality of input frames compriseconsecutive frames having same image characteristics, defines aplurality of frame indexes corresponding to the consecutive frames asthe same indexes, and determines a plurality of consecutive repeatedframes as repeated frames having same image characteristics when theplurality of consecutive repeated frames are comprised in the pluralityof input frames comprise.
 15. The image processing apparatus as claimedin claim 12, wherein the image mode comprises a first film mode and asecond film mode: when a current first group of consecutive frameindexes of the plurality of frame indexes indicates imagecharacteristics, the control unit determines that the current image modeas the first film mode; and when it is detected that a second group ofconsecutive frame indexes indicates second image characteristics, thecontrol unit switches the current image mode from the first film mode tothe second film mode.
 16. The image processing apparatus as claimed inclaim 11, wherein the mode determining circuit adaptively determines animage mode corresponding to a first group of frames of the input framesas a first film mode, and determines an image mode corresponding to asecond group of frames of the input frames as a second film mode, andthe mode determining circuit switches the current image mode from thefirst film mode to the second film mode, with the first film mode beingan M:N film mode, the second film mode being an L:N film mode, and L, Mand N are different positive integers.
 17. The image processingapparatus as claimed in claim 11, wherein as for a group of consecutiveframes, of the input frames, having the same image characteristics, themode determining circuit determines an image mode corresponding to thegroup of consecutive frames as a first film mode or a second film modeaccording to the number of the group of consecutive frames, and when theimage mode is the second film mode, the image generating unit calculatesthe plurality of motion vectors according to the motion estimationresult and a second group of frame indexes, of the plurality of frameindexes, corresponding to the second film mode.
 18. The image processingapparatus as claimed in claim 11, wherein the image generating circuitcomprises: a motion estimator, for generating the motion estimationresult; and an image generating unit, coupled to the motion estimator,when the image mode is a first film mode, the image generating unitcalculates a plurality of motion vectors according to the motionestimation result and a first group of frame indexes, of the pluralityof frame indexes, corresponding to the first film mode, respectivelygenerating the plurality of interpolated frames according to thecalculated plurality of motion vectors, and outputting the plurality ofinterpolated frames according to the plurality of input frames and theplurality of interpolated frames.
 19. The image processing apparatus asclaimed in claim 11, wherein when the motion estimation result indicatesa static video, the image generating circuit generates a firstinterpolated frame with reference to a first frame, of the input frames,corresponding to the image mode, and generates a second interpolatedframe with reference to a second frame, of the input frames,corresponding to the image mode, with the first frame and the secondframe being corresponding to the same frame indexes.